This invention relates generally to magnetic field sensors, and more particularly to apparatus having a plurality of orthogonally disposed optical fiber interferometers for determining the gradient of a magnetic field.
Magnetometers of the flux-gate or gas types have long been used to measure the Earth's magnetic field. For the detection of a magnetic local anomaly, however, the measurement of the spatial magnetic field gradient is of interest as well as the absolute magnitude of the field itself. Devices used in such measurements are referred to as "gradient field" magnetometers or simply gradiometers.
The most recent advances in the art of gradiometry utilize superconducting quantum interference devices (SQUID's) which are capable of detecting magnetic fields as small as 10.sup.-11 or 10.sup.-12 Gauss in the laboratory (see Giallorenzi et al, "Optical Fiber Sensor Technology," IEEE Journal of Quantum Electronics, Vol. QE-18, No. 4, April 1982, pp. 626-665). Nevertheless, SQUID's are often substantially less sensitive in the field and require cryogenic instrumentation for their operation, thus, severely limiting the conditions under which they can be effectively utilized.